The present invention relates to an LSI (large scale integrated) package having a multilayer ceramic substrate mounted densely with a plurality of integrated circuit (IC) chips.
High density LSI packages using alumina ceramic substrates are in use recently in high performance computers. The package includes densely wired layers formed on the upper surface of the ceramic substrate, a number of IC chips mounted densely on the upper surface of the top wiring layer, and a plurality of pin-shaped input/output (I/O) terminals arranged in matrix form on the lower surface of the ceramic substrate. Since the ceramic substrate has a thermal expansion coefficient well matching that of the silicon, which is the main component of each IC chip, these IC chips can be directly adhered to the substrate. As a result, the high density mounting of the IC chips on the substrate can be facilitated. By arranging the I/O terminals in matrix form throughout the whole lower surface of the substrate, it also facilitates an increase in the number of the I/O terminals per package to achieve higher density and integration of LSI packages. The alumina ceramic substrate is most suitable to sufficiently support such I/O terminals arranged in a matrix fashion.
However, the manufacturing yield of such an LSI package is not very high, because high density and fine formation are required for the wiring formed inside the alumina ceramic substrate. In other words, it is not quite possible to form the wiring completely despite full and meticulous care and control in manufacture.
Changes in the design may often become necessary after the design and manufacture of multilayer circuit substrates have been completed. Such a change in design requires a change in wiring. Therefore, a structure which permits such a repair and remodelling or wiring on the multilayer circuit substrate becomes desirable.
One example of such a change or repair technique for the wiring between plural numbers of IC chips is proposed in an article entitled "IBM Multichip Multilayer Ceramic Modules for LSI Chips--Design for Performance and Density" by BERNARD T. CLARK et al in the IEEE Transaction on Components, Hybrids and Manufacturing Technology, Vol. CHMT-3, No. 1, Mar. 1980 issue, pp. 89-93.
Although such a technique may be effective for the change or repair of the wiring between the IC chips, it is not so for the repair of the wiring between the IC chips and pin-shaped I/O terminals mounted on the lower surface of the substrate. This is because the conventional type substrate has no special wiring to connect a specific IC chip terminal and a specific I/O terminal when there occurs a manufacturing defect in the connection of the two terminals.
It is not necessarily impossible to bore a hole from the upper surface of the conventional type ceramic substrate to the lower surface thereof for passing the wire therethrough, but this is not a realistic solution in view of the difficulties arising in the substrate manufacture and of the excessively lowered wiring density.